This invention relates to processes for producing slow-release powders. In one aspect, this invention provides a process for producing a slow-release powder by first mixing a long-chain compound with a slow-releasable substance and then mixing the resulting mixture with urea. In another aspect, the invention provides a process for producing a slow-release powder by first mixing a long-chain compound with a slow-releasable substance, then mixing the resulting mixture with urea, and finally exposing the resulting urea adduct to radiation.
Slow-release powders permit various active ingredients such as perfumes, insect control agents, rust inhibitors, mold inhibitors and antibacterial agents to be slowly released over a prolonged time, thereby expanding the application field of those substances. The use of slow-release powders has been expanding these days as an adjunct to improvements in the quality of national life.
Known clathrates (hereinafter sometimes referred to as "adducts") capable of incorporating various substances include hydroquinone, deoxycholic acid, perhydrotriphenylene and cyclodextrins. The last-mentioned cyclodextrins form clathrates in powder form that are fairly high in their ability to include substances. However, it is not easy to form slow-release powders with cyclodextrins since the steps of incorporating slow-releasable substances and drying the mixture to obtain a powder are quite time-consuming. Furthermore, compared to urea used in the present invention, cyclodextrins are low in their ability to include substances and yet they are expensive.
The present inventors conducted intensive studies in order to develop an economical technique for producing slow-release powders having longer life and, as a result, they have succeeded in attaining this objective by using a mixture of urea and a long-chain compound, which idea has not been conceived of in the light of conventional clathrates including slow-releasable substances.